A panel of medical specialists recommended Thursday that the Food and Drug Administration reject a kidney cancer drug developed by Aveo Pharmaceuticals Inc., cutting the Cambridge company’s stock price nearly in half and dimming prospects for a medicine once considered promising for patients.

The surprise 13-to-1 vote against approving the experimental capsule, called tivozanib, delivered a blow to Aveo, which last fall restructured its operations to concentrate on the cancer drug. While the advisory panel’s action is not binding, the FDA rarely overrides such recommendations. The agency is expected to render its decision by July 28.

“This is disappointing for patients, because it would certainly be a step forward in quality of life,” said Dr. David F. McDermott, a kidney cancer specialist at Beth Israel­ Deaconess Medical Center in Boston and leader at the Dana-Farber Harvard Cancer Center, who advised Aveo on the drug. When it was given to a dozen patients locally to identify who might benefit, McDermott said, tivozanib proved as effective but less toxic than kidney cancer medicines now on the market.

But advisory panel members were concerned by the results of a late-stage clinical trial of 517 patients, which compared Aveo’s drug against Nexavar, akidney cancer treatment co-marketed by Onyx Pharmaceuticals Inc. and Bayer HealthCare Pharmaceuticals Inc. While tivozanib met its goal of slowing progression of the disease, formally known as renal cell carcinoma, patients taking Nexavar had better overall survival rates.

Get Business Headlines in your inbox:

The Globe's latest business headlines delivered every morning, Monday through Friday.

Despite the overwhelming vote by the Oncologic Drugs Advisory Committee, executives at Aveo were quick to insist they planned to continue pushing forward with the kidney cancer drug in hopes of eventually winning permission to sell it.

“We remain confident in the efficacy, safety, and tolerability of tivozanib in renal cell carcinoma patients,” Aveo chief executive Tuan Ha-Ngoc said in a statement.

“We are committed to the renal cell carcinoma patient community and will work closely with the FDA to address the issues discussed by the panel.”

Ha-Ngoc did not want to comment beyond the prepared statement, according to a company spokesman, who said Aveo officials would keep quiet as they await the FDA’s ruling.

In an interview late last year, Ha-Ngoc said the fortunes of 11-year-old Aveo were tied to tivozanib.

The company was positioning the capsule “to be among the standard of care” used by doctors in fighting kidney cancer, he said, and planned to boost the workforce to 300 employees from 225 by the end of 2013 if it was approved.

“Most of our resources need to be devoted toward approval and commercialization” of the kidney cancer treatment, he said. “So the number one, two, and three priorities of the company now is to get it to the patients.”

Aveo filed an application for approval with the FDA in September, along with its partner, the Japanese drug maker Astellas Pharma Inc., which would sell the medicine in Europe.

If approved, tivozanib would enter a market for kidney cancer drugs estimated at more than $2 billion a year worldwide.

There are currently at least five other approved therapies to treat renal cell carcinoma in the United States. While none cure the disease, they all extend — and improve the quality of — patients’ lives.

More than 60,000 Americans are diagnosed with kidney cancer each year and more than 13,600 die from it, according to the National Cancer Institute.

That suggestion sent Aveo’s shares tumbling more than 30 percent Tuesday in trading on the Nasdaq stock exchange. After the advisory panel vote Thursday, the stock plunged an additional 49.62 percent to $2.65 a share. Overall, the stock has lost more than 81 percent of its value since last summer.

McDermott, the Beth Israel Deaconess oncologist, said the design of the late-stage clinical trial might have been a problem for the FDA panel. Tivozanib was paired against Nexavir rather than the most-prescribed US kidney cancer drug, Sutent, sold by Pfizer Inc., he said.

In addition, he said, patients taking Nexavir in the trial survived slightly longer than those taking tivozanib. But he said some patients in the former group may have been given tivozanib after their disease progressed more, making the clinical study’s findings less straightforward.

“I would have preferred that [tivozanib] went up against the market leader and won,” McDermott said.

“But that being said, I think the patients will lose out if they don’t have access to this drug, which is as effective and less toxic than the other drugs on the market.”

BostonGlobe.com complimentary digital access has been provided to you, without a subscription, for free starting today and ending in 14 days. After the free trial period, your free BostonGlobe.com digital access will stop immediately unless you sign up for BostonGlobe.com digital subscription. Current print and digital subscribers are not eligible for the free trial.

Thanks & Welcome to Globe.com

You now have unlimited access for the next two weeks.

BostonGlobe.com complimentary digital access has been provided to you, without a subscription, for free starting today and ending in 14 days. After the free trial period, your free BostonGlobe.com digital access will stop immediately unless you sign up for BostonGlobe.com digital subscription. Current print and digital subscribers are not eligible for the free trial.